1. Field of the Invention
The present invention concerns a gearbox for a wind turbine.
In particular, the present invention concerns a gearbox for a wind turbine which consists of ring wheel unit provided in a housing; a driving shaft designed to be coupled to the rotor of the wind turbine and a single main bearing or a pair of main bearings which support the driving shaft such that it can be rotated in the housing, whereby the ring wheel unit is formed of a sun wheel, a planet wheel, ring wheel which is fixed to the housing in a non-rotating manner and a planet carrier which is rigidly fixed to the driving shaft.
2. Discussion of the Related Art
Such gearboxes for wind turbines are already known, whereby the driving shaft is coupled to the rotor of a wind turbine and whereby the sun wheel of the gear unit drives for example a generator.
In the conventional embodiments, the housing of the gearbox is made of several pieces, whereby a first part of the housing is for example a part of the supporting structure in which a couple of main bearings are provided directly in the seatings and whereby a second part of the housing is screwed onto the supporting structure, which part comprises the actual ring wheel unit.
It is also known to embed the main bearings as well as the ring wheel unit in a separate housing which is provided on the supporting structure afterwards.
These are what are called integrated main bearings.
In case of a further integration, the pair of main bearings is replaced by only a single main bearing, such as for example a double cone bearing.
The aim is that the main bearing or the pair of main bearings absorb the loads on the driving shaft due to the aerodynamic wind load as well as the rotor weight and transmit these directly or via the housing of the gearbox to the supporting structure of the wind turbine.
A disadvantage of the known embodiments is that, while the wind turbine is operational, the main bearings are subject to a certain elastic deformation under the influence of the rotor loads, which inevitably results in a certain play in the main bearings, which will cause an alignment error at the ring wheel unit which hinders the good working of the ring wheel unit.
For, a result of the above-mentioned alignment error is that the plays between the flanks of the teeth of the gear wheels can be restricted in some cases or can be entirely absent or, the other way round, may increase.
A disadvantage of all this is that an uneven load of the gear wheels is obtained and that the normal interplay of forces between the gear wheels is disturbed, which will result in the gear wheels and the bearings of the planet wheels being overloaded.
Also, the present invention aims to remedy one or several of the above-mentioned and other disadvantages.